The historical trend in magnetic recording technology has been to continuously increase the density of recorded data. With increases in linear data densities, have come higher linear recording velocities and a requirement for increased frequency response in both read/write heads and their associated electronics. Furthermore, increases in track density have required that the heads exhibit narrower pole tips.
Thin film processing and photolithography have been employed to accurately define magnetic head structure geometries. Until recently, thin film heads have been comprised of a single or multi-turn winding around which, a thin magnetic core of material is disposed. In U.S. Pat. No. 4,651,248 to Shiiki et al., a thin film magnetic head is described which employs a spiral conductor coil disposed between first and second magnetic layers. In U.S. Pat. No. 4,241,367 to Nomura et al., a multi-track thin film magnetic head is described wherein a plurality of individual head structures are formed on a single substrate. In U.S. Pat. No. 4,814,921, to a thin film magnetic head is described which includes a plurality of superposed magnetic films and intermediate layers which may be ferromagnetic, non-magnetic or anti-ferromagnetic.
Other examples of thin film magnetic heads may be found in U.S. Pat. No. 4,799,118 to Yamata et al., U.S. Pat. No. 4,277,808 to Nagaki et al., U.S. Pat. No. 4,306,215 to Jeffers and Japanese Patent 62-257,610.
Modern thin film heads are being applied to higher and higher data rate applications The resulting higher frequencies have increased eddy current losses in such heads. Others, have coped with the eddy current loss problem by proposing that thin film heads be constructed of layers of magnetic material with interspersed insulating films, for instance, see "Integrated Magnetic Recording Heads", Lazzari et al., IEEE Transactions on Magnetics, Vol. Mag-7, No. 1, March, 1971, pp. 146-150; and Japanese Patent 64-39608.
Experience with thin film magnetic heads constructed as suggested by Lazzari et al. has indicated that their structural integrity is not optimum Because the insulating films are deposited on intermediate magnetic films by either sputtering or chemical vapor deposition, the resulting combined layers exhibit built-in stresses which impair the head's structural integrity.
Eddy current effects in magnetic thin film heads are not a significant factor when the required frequency response of the head is 10 MHz or less. At higher frequencies, such losses become significant and radically affect the performance of the head. At such higher frequencies, the permeability of the magnetic thin films are adversely effected. This is demonstrated in "Permeability of Narrow Permalloy Stripes", by Feng et al., Transactions on Magnetics, Volume MAG-13, No. 5, September 1977, pages 1521-1523 where it is shown that above 10 MHz, the permeability of permalloy exhibits a steep fall-off.
Accordingly, it is an object of this invention to provide a thin film magnetic head having improved high frequency response characteristics and good physical integrity.
It is another object of this invention to provide an improved thin film magnetic head wherein the components of the head are chosen to be physically compatible.